[R-sig-Geo] Count frequency in raster stacks

[Robert J. Hijmans]

Here is a more direct (and safer) way:

library(raster)
set.seed(0)
r <- raster(nrows=22, ncols=20, xmn=-58, xmx=-48, ymn=-33, ymx=-22)
s <- stack(lapply(1:5, function(x) {setValues(r, round(runif(22 * 20,
min=0, max=600), digits=0))}))


intervals <- seq(0, 600, 100)

x <- cut(s, intervals, include.lowest=TRUE)
freq(x, merge=TRUE)



On Wed, Feb 17, 2016 at 4:54 PM, Thiago V. dos Santos
<thi_veloso at yahoo.com.br> wrote:
> Hi Lyndon,
> You were right - it worked like a charm. Thank you so much. Greetings, -- Thiago V. dos Santos
> PhD studentLand and Atmospheric ScienceUniversity of Minnesota
>
>     On Wednesday, February 17, 2016 5:04 AM, Lyndon Estes <lyndon.estes at gmail.com> wrote:
>
>
>  Hi Thiago,
> Something like this should work:
> s <- stack(lapply(1:5, function(x) {  r <- raster(nrows=22, ncols=20, xmn=-58, xmx=-48, ymn=-33, ymx=-22)  r[] <- round(runif(22 * 20, min=0, max=600), digits=0)  r}))
> intervals <- seq(0, 600, 100)
> vals <- sapply(1:nlayers(s), function(x) {  # x <- 1  # Count frequencies and calculate percentage  ## note: don't use df or t as object names--they are both functions  tab <- table(cut(as.vector(s[[x]]), intervals, include.lowest=TRUE))  # ncells <- length(Which(!is.na(s[[x]]), cells = TRUE)) # alternative  ncells <- sum(!is.na(s[[x]][]))  DF <- data.frame(round(tab, digits=2))[, 2]  })
> # set up a column that decribes the rainfall bins/intervalsints <- cbind(intervals[-length(intervals)], intervals[-1])bins <- apply(ints, 1, function(x) paste(x, collapse = "-"))
> # bind to outputcbind.data.frame(bins, vals)
>
> On Wed, Feb 17, 2016 at 4:27 AM Thiago V. dos Santos <thi_veloso at yahoo.com.br> wrote:
>
> Hi all,
>
> I am trying to count the frequency of values in raster objects based on specified intervals. For example, I have a raster storing monthly rainfall totals ranging from 50 to 600 mm. And I need to know how many values fall in the interval 0-100, how many on 101-200, 201-300 and so on.
>
> I managed to do it in a single raster:
>
> require(raster)
>
> ## scratch a raster and fill some random values
> r <- raster(nrows=22, ncols=20, xmn=-58, xmx=-48, ymn=-33, ymx=-22)
> r[] <- round(runif(22 * 20, min=0, max=600), digits=0)
>
> # Count raster cells (excluding NA's) and set intervals
> ncells <- sum(!is.na(r[]))
> intervals <- seq(0, 600, 100)
>
> # Count frequencies and calculate percentage
> t <- table(cut(as.vector(r), intervals, include.lowest=TRUE)) / ncells * 100
> df <- data.frame(round(t, digits=2))
>
>
> However, how can I do the same for a raster stack, storing the count of each layer in a column of the resulting data frame?
> Thanks in advance,
>  -- Thiago V. dos Santos
>
> PhD student
> Land and Atmospheric Science
> University of Minnesota
>
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